Among significant uses of fuel in the U.S. economy lie the operation of foundries and steel mills. In these operations, natural gas is customarily used for ladle drying and preheating, in addition to other tasks. Gas has been used primarily in these industries for the past two decades, because it has been low in cost and it has offered simplicity of operation, with minimum pollution control requirement. Nonetheless, drying and preheating of ladles is less than 10 percent efficient in the use of such high quality fuels. Due to the recent energy crisis and the decline in natural gas reserves in the U.S., It has become apparent that many of these industries will have to forego the use of gas for other fuels and employ more efficient processes.
The most plentiful alternative fuel in the United States today is coal. Coal comes in many varieties ranging from high volatile-high sulfur content to low volatile-low sulfur content coal all with a variety of ash content. Because of the nature of the fuel, several environmental problems may be encountered in applying it to foundries and steel mill operations. The principal problems are the gaseous emissions primarily found in the form of sulfur oxides and particulate emissions formed from the ash content of the coal.
The present invention is conceived to achieve minimum environmental impact, while allowing the use of coal and other fuels for several tasks in foundries and steel mills. The principal task herein comprises the preheating of ladles. These ladles are large steel bucket-like containers with refractory liners into which molten steel is poured, generally from electric arc or other type of furnaces. In order to minimize the cooling of the molten steel so that further pouring operations can be conducted, it is necessary to preheat the ladle to such temperature that little, if any, heat is lost from the molten steel into the ladle. As indicated above, the preheating operation is presently performed primarily with natural gas and it is thus proposed that this task be modified so that primarily a coal fuel and, secondarily, oil may be used.
Among gas fired ladle heaters are the Burnham blue flame industrial burner. It is currently used, for example in the preheating of ladles of the Shah-Milwaukee Steel Division, Grede's Foundries, Inc. In such instances, the pour ladle is disposed horizontally, relative to the industrial wall burner, an adapted refractory burner block having an appropriate hot gas return tube. Such gas fired ladle heaters operate at approximately 1800.degree. F., although they may be operated at either high or low fire.
Ladle drying and preheating, and ladle-heating efficiency has also been made the subject of a group research proposal entitled Development of Lower-Cost Ladle-Heating Practices by the Battelle Columbus Laboratories as of Mar. 31, 1976; Proposal No. 926-8-3952. In none of the aforesaid has specific attention been given to adaptation of a fluidized mother bed, ladle heating system, utilizing apparatus and method of the type set forth in my co-pending application, Ser. No. 799,238, filed May 23, 1977, and entitled METHOD AND APPARATUS FOR HEAT-TREATING OF METAL SHAPES OR CASTINGS.